People are Strange OR Quarks, Glue, and Electrons, too: That’s What Little Boys and Girls Are Made Of! Jeff Martin University of Winnipeg Jan. 25, 2006 Skywalk Lecture Series

A Couple of Big Questions People have long asked: What is the world made of? What holds that stuff together? Let’s pick some object and zoom in on it.

The Big Apple courtesy NOVA (PBS.ORG)

Note: one cannot see this with a normal microscrope.

a carbon atom

protons and neutrons are inside

Humans have not yet determined how to “see” anything smaller than a quark.

metres

The Standard Model

Ingredients in the Standard Model

A “Simple” Recipe: How to Make a Proton u u d Quark charge: u+2/3e d-1/3e e 2 “up” quarks + 1 “down” quark makes a proton.

However, we know it’s all more complicated than that… u u d Quarks are held together in a bag by gluons (carriers of the strong force) g g glue: bleccch. Not too tasty!

The Proton: The Disturbing Discovery u u d s s Zooming in, we begin to see virtual quarks. In particular, STRANGE quarks Proton  uud + g … The ‘‘Sea’’ Wow, it’s really complicated!

And if you really zoom in…

Previous Data on Strange Quarks 70% regular stuff (up and down quarks) 30% strange quarks!!!! About 50 pounds of me is strange!

How do you measure something like that? Do an experiment: –Fire electrons at a proton target and look at the way that they scatter from it. –That’s the way the atomic nucleus was discovered! (Rutherford, 1911) And how does that tell you about strange quarks? –It doesn’t: you actually have to measure using the weak force and compare to “regular” experiments.

The Experiment target In our experiment, the electron is moving at % the speed of light. Note: University of Winnipeg does not have a gigantic electron accelerator.

Ever wonder what physics professors do on their summer “vacation”?

A Particle Physics Experiment: “Gee-Zero” Caltech Carnegie-Mellon William+Mary Grinnell College Hampton IPN-Orsay ISN-Grenoble Kentucky LaTech NMSU JLab TRIUMF UConn U Illinois U Manitoba U Maryland U Mass UNBC VPI Yerevan and the University of Winnipeg Jefferson Lab, Newport News, VA, USA

superconducting magnet detectors (Ferris wheel) target (some protons) G 0 Experiment electrons

The Question How much of the proton’s magnetism comes from strange quarks? The Answer (from G 0 ) About 5% And by the way: that is AMAZING! –(way bigger than one would naively expect)

Strange Quarks and the Economy “The results, reported in this week's Physical Review Letters, showed that this was far greater than had been predicted. In particular, some 5% of a proton's magnetism is contributed not by the host quarks but by visiting strange quarks that have popped out of nowhere.” “So, next time you have an MRI scan, remember that part of the picture depends on something that isn't really there. Strange, eh?”

A Strange New World We now know that strange quarks play a bigger role in the properties of the proton than anyone ever thought was possible! Still more work to do… this summer. My website: nuclear.uwinnipeg.ca Other resources: particleadventure.org This work is funded by: Natural Sciences and Engineering Research Council of Canada